The present invention is broadly concerned with a control valve for a medical fluid infusion device. More particularly, it is concerned with a positive pressure actuated flow control valve that permits flow of a liquid from a reservoir, through a cannula and into a patient, while resisting reflux.
Medical infusion therapy employs peripheral and central intravascular devices such as venous and arterial catheters as well as peripherally inserted central venous catheters to deliver fluids, blood products, and pharmaceuticals, including antibiotics and biologics as well as parenteral nutrition. Intravascular devices may also be coupled with pressure monitoring systems.
Regardless of the location of the insertion site of the catheter or the placement of its terminus, intravascular devices, and central venous catheters (CVCs) in particular, are subject to retrograde blood flow into the catheter lumen whenever the pressure in the patient's vascular system exceeds resistance at the supply end of the catheter. This may occur, for example, when fluid pressure drops because a gravity supply source is empty, when an injection port is opened by removal of a syringe, or when a stopcock is opened.
Retrograde blood flow is known to contribute to complications such as catheter-related septicemia, venous thrombosis, superior vena cava syndrome, pulmonary embolism and phlebitis. Thrombus formation may cause partial or complete occlusion of the catheter. Partial occlusion results in impaired sampling and fluid administration. Complete occlusion causes the catheter to lose patency, necessitating removal and replacement, so-called “unscheduled restarts”.
Catheter reflux-induced thrombosis is not merely a mechanical complication, since it appears to be a major contributor to catheter related bloodstream infections associated with the use of long term catheters. Such infections are associated with increased morbidity and mortality as well as increased health care costs associated with extended hospitalization.
Attempts have been made to develop improved intravascular devices in order to address the mechanical and infectious complications previously described. Peripherally inserted central venous catheters (PICCs) are known to reduce the incidence of thrombosis and phlebitis as well as commonly reported central catheter-related infections. However, PICC devices are not suitable for all applications, particularly where the solution to be administered has high osmolarity or may be a pH irritant. And patients with PICC infusion still experience thrombus formation and phlebitis at statistically significant levels.
Guidewire assisted exchange has also been employed to achieve a lower rate of mechanical complications following insertion of replacement catheters. However, patients may experience bleeding, hydrothorax and subsequent catheter related infections.
In-line filters have also been employed to reduce infusion-related phlebitis. However, they have not been found to prevent intravascular device-related infections. And use of such filters is not regarded as mechanically favorable, since solution filtration may be accomplished more efficiently prior to infusion and the filters themselves are subject to blockage.
Impregnated catheters and needle-free devices have also been employed. Although they have not yet been thoroughly evaluated, antimicrobial coated or impregnated catheters appear to be more effective for central venous use than for peripheral use. There are concerns, however, that they may foster development of resistant bloodstream pathogens. Needle-free infusion systems also have not yet been fully studied, although one investigation has shown survival of skin flora in needleless infusion systems.
There have also been attempts to develop methods of using conventional intravascular devices in order to prevent catheter-related thrombus formation and to maintain catheter patency. Turbulent positive pressure flushing with anticoagulant heparin solution, use of thrombolytic agents such as urokinase, streptokinase and t-Pa, and prophylactic warfarin administration have all been employed.
However, some in vitro studies have suggested that heparin flush solutions may serve to enhance growth of Coagulase-negative staphylococci (CoNS). The United States Public Health Service, Centers for Disease Control and Prevention (CDC) has cited CoNS as “the primary pathogen causing catheter-related infections”. It has recommended clinical trials to evaluate the practice of flushing with anticoagulant solutions to prevent catheter-related infections. The CDC has also cited an association between use of low dose heparin and thrombocytopenia and thromboembolic and hemorrhagic complications.
All of the preventive methods that are currently available appear to contribute in some manner to general health care delivery problems, such as delay, increased requirements for nursing care, pharmaceutical and supply costs, increased patient risk and discomfort.
Accordingly, there is a need for an improved intravascular device that will resist retrograde blood flow and thereby reduce rates of thrombus formation, catheter-related blood stream infection, and unscheduled restarts and thereby extend catheter indwelling times.